Since the energy in a stream of water varies as the cube of its speed, it is desirable to locate ‘free-stream’ tidal energy devices where the stream is fastest. For example, headlands form obstacles to a tidal stream which cause the stream to accelerate as it passes around them. Also, because of boundary layer effects, more energy is available at a distance above the sea bed. However, already-known ‘free-stream’ arrangements for taking advantage of the fact that water streams tend to be faster close to the surface, require either expensive seabed foundations for rugged permanent structures, which may also impede navigation, and or the use of divers for retrieval of gear when this is required for maintenance purposes.